Currently, in cameras for broadcast use such as television cameras, cameras for business use and cameras for measurement use, prisms are used in a color separation optical system for allowing optical dispersion in a plurality of directions, to form captured optical images on solid-state image pickup elements provided on their emission planes through, for example, dispersion into three primary colors, i.e., blue, red and green. The optical images formed on the solid-state image pickup elements are subjected to photoelectric conversion, and amplified and processed by a video circuit to obtain predetermined video signals.
Such a color separation optical system requires precisely aligning each of three solid-state image pickup elements in relation to six axes X, Y, Z, θx, θy and θz with respect to an optical axis, as shown in a perspective view in FIG. 2 illustrating adjustment directions of a solid-state image pickup element, before bonding and fixing the solid-state image pickup elements to a color separation prism.
A prior known imaging apparatus with bonded and fixed solid-state image pickup elements is disclosed in Prior Art 1: Japanese Laid-Open Utility Model Publication No. 62-47289, titled “ATTACHMENT PLATE FOR COLOR SEPARATION OPTICAL SYSTEM”.
Prior Art 1 is described with reference to drawings. FIG. 10(a) is a plan view in which solid-state image pickup elements are attached to a color separation prism in Prior Art 1 via spacers on attachment plates, FIG. 10(b) is a side view in which a solid-state image pickup element is attached to the color separation prism in Prior Art 1 via spacers on an attachment plate, FIG. 11 is an enlarged view of attached portions in Prior Art 1, and FIG. 12 is an enlarged view of attached portions illustrating a variant of the spacer in Prior Art 1.
As shown in FIG. 10, attachment plates 102 are attached so as to sandwich a color separation prism 101 of a color separation optical system 105, and three solid-state image pickup elements 103 are each aligned in relation to the aforementioned six axes, and thereafter, bonded and fixed to the attachment plates 102 via two spacers 104.
In FIG. 11, emission-side end faces of the attachment plates 102 attached to the color separation prism 101 form inclined faces 102A inclined with respect to an emission optical axis. On the other hand, the spacers 104 each have a vertical face 104A formed on the right side and an inclined face 104B formed on the left side, which is inclined with respect to the emission optical axis. As can be seen from FIG. 11, the inclined faces 102A and 104B are formed at approximately the same inclination angle. In addition, gaps required for applying an adhesive are left between the inclined faces 102A and 104B and between the vertical face 104A and a light reception plane-side surface of the solid-state image pickup element 103.
The color separation optical system 105 with such a structure is mounted on an unillustrated 6-axis adjustment jig to adjust the solid-state image pickup element 103 in three axial directions X, Y and Z and three axial rotation directions θx, θy and θz as shown in the perspective view in FIG. 2 illustrating adjustment directions of a solid-state image pickup element package, and thereafter, the vertical faces 104A and the inclined faces 104B of the spacers 104 are applied with an adhesive and inserted into the gaps between the inclined faces 102A of the attachment plates 102 and the solid-state image pickup element 103.
With such a configuration, even if the gaps between the end faces of the attachment plates 102 and the light reception plane-side surface of the solid-state image pickup element 103 are uneven, the spacers 104 are structured to have at least one inclined side face, so that the inclined faces 104B of the spacers 104 are brought into surface contact with the inclined faces 102A of the attachment plates 102, and therefore it is possible to bond them together by using the pair of spacers 104.
In addition, if, as a result of adjustment by the 6-axis adjustment jig, the inclined faces 104B and 102A are inclined at different inclination angles as shown in FIG. 12, it is possible to bring the inclined faces 104B into line contact with the inclined faces 102A and bond them together.
Another example is disclosed in Prior Art 2: Japanese Laid-Open Patent Publication No. 5-37943, titled “SOLID-STATE IMAGE PICKUP APPARATUS”.
Prior Art 2 is described with reference to drawings. FIG. 13 is a configuration diagram of a solid-state image pickup apparatus in Prior Art 2, FIG. 14 is an enlarged cross-sectional view of attached portions in Prior Art 2, and FIG. 15 is an enlarged cross-sectional view of attached portions illustrating a variant of a solid-state image pickup element in Prior Art 2.
In FIG. 13, a solid-state image pickup element 203 is fixed on each emission plane of a color separation prism 201 via a pair of connecting/fixing members 204 by applying an adhesive between the color separation prism 201 and the connecting/fixing members 204 and between the connecting/fixing members 204 and the solid-state image pickup element 203, such that the solid-state image pickup element 203 is sandwiched by the connecting/fixing members 204. The color separation prism 201 is coated with a light-shielding paint 202 except for its emission planes.
Filter glass having a characteristic of selectively transmitting ultraviolet light therethrough or membranes for selectively transmitting ultraviolet light therethrough, which are formed by evaporating an optical multilayer film onto white or blue sheet grass, are used for the connecting/fixing members 204 for connecting and fixing together the color separation prism 201 and the solid-state image pickup element 203 placed in the vicinity of an emission plane thereof as shown in FIG. 14, so that only light required for curing the ultraviolet-curable adhesive is transmitted and light in a range that is sensed by the solid-state image pickup element 203 is cut off; the ultraviolet-curable adhesive 205 is applied between the color separation prism 201 and the connecting/fixing members 204 and between the connecting/fixing members 204 and the solid-state image pickup element 203, and after using an unillustrated 6-axis adjustment jig to adjust the solid-state image pickup element 203 in three axial directions X, Y and Z and three axial rotation directions θx, θy and θz as shown in FIG. 2, the adhesive 205 is cured through irradiation with ultraviolet light, thereby connecting and fixing together the color separation prism 201, the connecting/fixing member 204 and the solid-state image pickup element 203.
In addition, if, as a result of adjustment by the unillustrated 6-axis adjustment jig, the solid-state image pickup element 203 is inclined as shown in FIG. 15, the applied ultraviolet-curable adhesive 205 is deformed and cured through irradiation with ultraviolet light, and therefore it is possible to connect and fix together the color separation prism 201, the connecting/fixing member 204 and the solid-state image pickup element 203.
In general, the adhesive has a characteristic of shrinking in volume by several percents when cured, or so-called curing shrinkage, which impairs positional precision at the time of fixation, but the curing shrinkage of an adhesion layer can be counterbalanced by movement of the connecting members, whereby it is possible to cure it while maintaining precision so as not to change the positional relationship between a solid-state image pickup element and a prism block.
The above conventional methods for bonding and fixing a color separation prism and a solid-state image pickup element together, however, have a problem in that, if the amount of applied ultraviolet-curable adhesive is not uniform or ultraviolet light irradiation by the 6-axis adjustment jig is uneven, the curing shrinkage of the ultraviolet-curable adhesive also becomes uneven, so that the solid-state image pickup element is fixed in a position deviating from an original alignment position.
In addition, in cameras for broadcast use, cameras for business use and cameras for measurement use, the number of pixels in a solid-state image pickup element is increased, so that an area per pixel is decreased, and furthermore an imaging area is further decreased from ⅔, ½ or ⅓ inches, therefore the conventional bonding and fixing methods has a difficulty in maintaining high-definition images by preventing alignment error due to the curing shrinkage of the adhesive and positional change due to variations in ambient temperature during operation.
In view of the above-described present situation, the present invention provides a method of fixing a color separation prism and a solid-state image pickup element, wherein even if the amount of applied adhesive is nonuniform, or ultraviolet light irradiation is uneven, or the curing shrinkage of the ultraviolet-curable adhesive also becomes uneven, a positional deviation of the solid-state image pickup element is prevented, while dealing with an increase in number of pixels or reduction in size of the solid-state image pickup element without using a specialized member such as filter glass.